Not applicable.
Not applicable.
This invention relates to the synthesis and application of phenolic novolak modified resorcinolic resins.
The performance of rubber composites in articles such as tires, belts and hose products depends on numerous factors including the quality of adhesion between the rubber and reinforcing materials, and the mechanical properties of the cured rubber matrix in contact with the reinforcing materials.
The conventional method of optimizing the adhesion of the rubber to the reinforcement comprises a two-part adhesive system that includes a methylene donor and a methylene acceptor. The methylene donor generates methylene or methylol groups capable of reading or crosslinking with the methylene acceptor, which interacts with the rubber and reinforcing material with a resultant increase in adhesion of the rubber to the reinforcing material. Because the methylene donor and the methylene acceptor are compounded into the rubber, they can have a significant effect on the properties of the final rubber product.
The most commonly used methylene donors are hexamethylenetetramine (HEXA) and hexamethoxymethyl melamine (HMMM). Dihydric phenols, polyhydric phenols and phenolic novolak resins have been used in the rubber industry as methylene acceptors. For example, resorcinol is a widely used dihydric phenol methylene acceptor for bonding rubber to the reinforcing materials. Because resorcinol is a small molecule, it can become uniformly distributed in the rubber during the compounding, resulting in excellent physical, mechanical and steel cord adhesion properties of the cured rubber products. But the fuming associated with resorcinol at Banbury temperature conditions causes problems, particularly with the loss of product.
Phenolic novolak resins have long also been used by the tire industry as the methylene acceptor in the rubber compound formulations. When these phenolic novolaks are cured with the methylene donors, such as the HMMM or HEXA (HMT), they increase the hardness, stiffness, tear resistance, abrasion resistance, tensile strength and modulus of the cured rubber compounds. In general, phenolic novolaks are used as tackifying and reinforcing resins in the rubber compound formulations. But they are not used in steel wire skim rubber compound formulations due to slow cure and high hysteresis. The relatively slow cure and the relatively high heat generation of the phenolic novolak resins are, therefore, expected to affect the adhesion of tire cords with the rubber. In order to improve the service life of tires, it is important that the bond between the tired cords, such as the steel, and the vulcanized rubber be relatively strong. Resorcinol use in rubber compounding formulations provides such a bond between the steel and rubber. This is due to the high reactivity of resorcinol towards the methylene donor and also produces a low hysteresis rubber compound.
Therefore, there is a need for an improved methylene acceptor for use in rubber compounding applications. Preferably, the methylene acceptor has a relatively shorter cure time so that improved rubber compositions can be obtained.
Embodiments of the invention fulfill the aforementioned need in one or more of the following aspects. In one aspect, the invention relates to a vulcanizable rubber composition which comprises (I) a rubber component selected from natural rubber, synthetic rubber or combinations thereof; (II) a methylene donor compound which generates formaldehyde upon heating,; and (III) a methylene acceptor compound comprising a phenolic and resorcinolic novolak resin blend represented by the following structures: 
where n is equal to or greater than 1, and m is equal to or greater than 1. The phenolic and resorcinolic novolak resin blend generally has a weight ratio of phenolic resin to resorcinolic resin between about 95:5 to 5:95. In some embodiments, the phenolic and resorcinolic novolak resin blend is prepared by prepared by (a) reacting one or more phenolic compounds represented by the following formula: 
where R is selected from the group consisting of H, an alkyl group chain of 1-16 carbon atoms and an aralkyl group of 8-12 carbon atoms with an aldehyde in the presence of an ortho directing catalyst and (b) combining with a resorcinol-formaldehyde novolak resin. Certain phenolic and resorcinolic novolak resin blends comprise (a) o-oxe2x80x2 phenolic methylene linkages in the range of about 25 to 96%; (b) o-pxe2x80x2 phenolic methylene linkages in the range of about 4 to 50%; (c) combined o-oxe2x80x2 phenolic methylene linkages and 4-4xe2x80x2 resorcinolic methylene linkages in the range of about 10-90%; and (d) p-pxe2x80x2 phenolic methylene linkages in the range of about 1 to 30%.
In other embodiments, the methylene acceptor is prepared by reacting (A) phenol and/or an alkyl phenol with (B) an aldehyde in the presence of (C) an ortho directing divalent metal salt catalyst to produce a high ortho phenolic novolak products containing at least 25% ortho-ortho phenolic methylene bridges and then (D) adding resorcinol or resorcinolic derivative or a meta-substituted phenol and then (E) reacting with an additional amount of an aldehyde. The resin blend made by such a process comprises the following structures: 
where n is equal to or greater than 1, and m is equal to or greater than 1. In some processes, the molar ratio of phenol and/or alkylphenol to formaldehyde is about 1/0.4 to 1/0.86; the molar ratio of resorcinol or resorcinol derivative or m-substituted phenol to formaldehyde is about 1/0.4 to 1/0.7. In other processes, the alkyl phenol is used to prepare the phenolic novolak resin, and the resin comprises o-oxe2x80x2 methylene linkage in the range of about 40 to 70%. In some processes, the alkyl phenol used to prepare the phenolic novolak is selected from para substituted alkyl chain containing 1 to 16 carbon atoms or aralkyl substituted phenols selected from the group consisting of p-cresol, p-tert-butyl-phenol, p-tert-octyl phenol, p-tert-butyl-phenol, p-tert-octyl phenol, p-tert-nonylphenol, p-nonylphenol, p-styrylphenol and pethylphenol. In other processes, the molar ratio of phenol and/or alkylphenol to aldehyde is between about 0.1:0.9 and about 0.9:0.1. In some processes, the aldehyde is formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, isobutyraldehyde, valeraldehyde, crotonoaldehyde, benzaldehyde, furfural, or a mixture thereof. In other processes, the resorcinolic derivative or meta-substituted phenol is selected from the group consisting of 2,4-dihydroxy benzophenone, 2,4-dihydroxy acetophenone, 4-styryl resorcinol, m-cresol, cashew nut shell liquid, phloroglucinol, 3-methyl-5-ethyl phenol, meta-isopropyl phenol, m-isoctyl phenol and 3,5-dimethyl phenol.
In some other embodiments, the methylene acceptor is prepared by reacting (A) one or more phenolic compounds represented by the following formula: 
where R is selected from the group consisting of H an alkyl chain of C1-C6 carbon atoms and an aralkyl group of C8-C12 carbon atoms with (B) an aldehyde in the presence of (C) an azeotroping solvent and (D) an ortho directing catalyst comprising a divalent electropositive metal compound selected from the group consisting of oxides, hydroxides, formates, lactates, acetates, benzoates, and mixtures of calcium, barium, strontium, magnesium, zinc, manganese, cobalt and lead; (E) then adding resorcinol or resorcinolic derivative or a preformed resorcinol-formaldehyde novolak resin. In some processes, the azeotrope solvent is selected from the group consisting of toluene and xylene. The resin blend made by the process (which can used as a methylene acceptor) comprises the following structures: 
where n is equal to or greater than 1, and m is equal to or greater than 1. Certain resin blends made by the process comprise (1) o-oxe2x80x2 phenolic methylene linkages in the range of about 25 to 98%; (2) o-pxe2x80x2 phenolic methylene linkages in the range of about 4 to 50%; (3) p-pxe2x80x2 phenolic methylene linkages in the range of about 1 to 30%; and (4) combined o-oxe2x80x2 phenolic methylene linkages and 4-4xe2x80x2 resorcinolic methylene linkages in the range of about 10 to 90%. Certain other resin blends comprise about 90 to about 98% o-oxe2x80x2 methylene bridges. In some cases, the resin blend has a weight ratio of phenolic resin to resorcinolic component between about 95:5 to about 5:95.
In other embodiments, the vulcanizable rubber composition further comprises a reinforcing material selected from the group consisting of nylon, rayon, polyester, polyamide, fiberglass, and steel. In some cases, the rubber composition is used in preparation of composite products for the manufacture of tires, power belts, conveyor belts, printing rolls, automobile floor mats, mud flaps for trucks or ball mill liners.
In another aspect, the invention relates to a vulcanizable rubber composition which comprises: (I) a rubber component selected from natural rubber, synthetic rubber or combinations thereof; (II) a methylene donor compound which generates formaldehyde upon heating; and (III) a methylene acceptor compound prepared by first reacting one or more phenolic compounds represented by the following formula: 
where R is selected from the group consisting of H, an alkyl group chain of 1-16 carbon atoms and an aralkyl group of 8-12 carbon atoms with an aldehyde in the presence of an ortho directing catalyst and then combining a resorcinol-formaldehyde novolak resin to obtain a phenolic and resorcinolic novolak resin blend.
Additional aspects of the invention and characteristics and properties of various embodiments of the invention become apparent with the following description.